1. Field of the Invention
The present invention relates to a method and an apparatus for cutting a semiconductor wafer and, more particularly to a method and an apparatus for cutting a semiconductor wafer, adhered to a mount tape, into individual pieces by a cutter.
2. Description of the Related Art
Generally, as shown in FIG. 7, a semiconductor element used for a semiconductor device is supplied by cutting a silicon wafer 12 (hereinafter referred merely to a xe2x80x9cwaferxe2x80x9d 12), on which a plurality of semiconductor elements 13 are formed, into individual pieces.
When the semiconductor elements 13 of the wafer 12 are initially cut into individual pieces, a back surface of the wafer 12 is adhered to a mount tape 100 mainly composed of a resin with an adhesive layer 14, as shown in FIG. 8.
Then, the mount tape 100 on which the wafer 12 is adhered is placed on a stage surface of a stage 102 and cut with a rotating blade 104 as shown in FIG. 9, wherein a predetermined gap H is maintained between the stage surface of the stage 102 and the rotating blade 104.
By cutting the wafer 12 while maintaining the predetermined gap H between the stage surface of the stage 102 and the rotating blade 104, as shown in FIG. 10, cut grooves 106 are formed by the rotating blade 104. While the semiconductor elements 13 of the wafer 12 are separated from each other by the cut grooves 106, the mount tape 100 is not completely cut and individual cut semiconductor elements are still adhered to the mount tape. Therefore, the cut semiconductor elements 13 are prevented from scattering during and/or after cutting, whereby the cutting operation and the post treatment are facilitated.
In this regard, the thickness of the wafer 12 has recently been reduced, resulting in a lowering of wafer strength. Thereby, it has been found that cracks or chipped portions are generated in the wafer 12 when cut by the rotating blade 104.
The inventors of the present invention believe that such cracks or chipped portions are caused by a shearing force applied to the wafer 12 when the wafer 12 is cut by the rotating blade 104, and have tried to cut the wafer 12 with a laser beam.
However, the inventors of the present invention have found that, if the laser beam is used for cutting the wafer 12 into individual semiconductor elements 13, the mount tape 100 is also cut into pieces.
The inventors then tried to cut the semiconductor elements 13 on the wafer 12 into individual pieces and half-cut the mount tape 100 with a laser beam, and found that it is necessary to delicately adjust an output of the laser beam if a desirable cut groove 106 as shown in FIG. 10 is to be formed and that the heat generation is problematic in the cutting of wafer with the laser beam, which means that the cutting of the wafer 12 with the laser beam is not industrially advantageous.
Although there are various problems in the prior art method for cutting the wafer 12 with the laser beam as described above, this method is advantageous because it is free from the generation of cracks and/or chipped portions caused by the cutting of wafer 12, since no large shearing force is applied onto the wafer 12 unlike the cutting with the rotating blade 104.
An object of the present invention is to provide a method for easily cutting a wafer with a laser beam.
The present inventors have studied the above-mentioned problems of the prior art and found that it is possible to cut the wafer while removing heat generated in a cut area during the cutting operation, if the laser beam cutter ejects a beam-like water jet having a predetermined width corresponding to a slit to be cut to an area of the wafer to be cut, while directing a laser beam axially through the beam-like water jet.
Also the inventors have found that, by using a mount tape in which is embedded a mesh-like member formed of material harder than a main resin component of the mount tape, it is possible, even though the mount tape is cut into pieces, to prevent the individual cut pieces from scattering about because the mesh-like member is not cut and connects the cut pieces with each other. Thus, the present invention was completed.
According to the present invention, there is provided a method for cutting a semiconductor wafer, the method comprising the following steps of: adhering a mount tape on a back surface of said semiconductor wafer, said mount tape comprising a resin base and a mesh-like member made of a material harder than that of said resin base and embedded in said resin base; and ejecting a beam-like liquid jet toward a front surface of said semiconductor wafer and simultaneously transmitting a laser beam axially through said beam-like liquid jet, so that said semiconductor wafer is cut into individual pieces by said laser beam together with said resin base of the mount tape, while said mesh-like member remains in its connected state. In this case, the pressure of said beam-like liquid jet and the output of said laser beam is determined in such a manner that said semiconductor wafer is sufficiently cut, while the mesh-like member of the mount tape is not cut, but remains in its connected state.
According to the present invention, since a liquid beam having a width corresponding to a desired slit width to be cut is ejected on an area of a wafer to be cut and, simultaneously a laser beam is axially directed through the beam-like liquid to the area of the wafer to be cut, it is possible to remove heat, generated during the cutting with the laser beam, by the beam-like liquid, as well as to minimize the shearing force applied to the wafer in comparison with a case wherein the wafer is cut with a rotating blade.
Further, according to the present invention, an assembly of a wafer adhered to a mount tape in which is embedded a mesh-like member formed of material harder than a main resin component of the mount tape is cut with a laser beam transmitted axially through the beam-like liquid jet ejected to have a width corresponding to a desired slit width to be cut.
When the wafer and the mount tape are cut as described above, a portion of the mesh-like member in the cut slit is not cut but left as it is. Therefore, the mesh-like member connects the individually cut pieces with each other to prevent the cut pieces from being scattered about. As a result, the cutting operation and the post treatment can easily be carried out.
The beam-like liquid jet is a pressurized pure water jet and focused so as to have a diameter in a range of 30 to 50 xcexcm, so that said semiconductor wafer cuts along a slit having a corresponding width.
The said mesh-like member is a glass cloth made of glass filament. In this case, the glass cloth comprises a plurality of lateral filaments and a plurality of transverse filaments substantially extending perpendicularly to the lateral filaments, so that the semiconductor wafer is cut along a slit which extends so as not to be in parallel to said lateral or said transverse filaments. In this case, the semiconductor wafer is preferably cut along a slit which extends at an angle of 30 to 60 degree to said lateral and said transverse filaments. A total thickness of the mount tape is in a range from 80 to 100 xcexcm and a diameter of the glass fiber is in a range from 20 to 90 xcexcm.
According to another aspect of the present invention, there is provided an apparatus for cutting a semiconductor wafer comprising: a mount tape comprising a resin base and a mesh-like member made of a material harder than that of the resin base and embedded in the resin base; first means for holding the mount tape, to which a back surface of the semiconductor wafer is adhered, second means for ejecting a beam-like liquid jet toward a front surface of the semiconductor wafer and simultaneously transmitting a laser beam axially through the beam-like liquid jet; and means for moving at least one of the first and second means, so that the semiconductor wafer is cut into individual pieces by the laser beam together with the resin base of the mount tape, while the mesh-like member remains in its connected state.